The video laryngoscope has significantly improved tracheal intubation for patients with difficult airways—an anatomical deviation that often results in failed intubation for surgical anesthesia or emergency rescue. In fact, the American Society of Anesthesiologists (ASA) revised its Practice Guidelines in 2013 to include video-assisted laryngoscopy as an initial approach to intubation of the difficult airway.
While revision of the ASA Practice Guidelines affirms a growing trend to establish video laryngoscopy as a routine standard procedure for tracheal intubation, data are conflicting as to whether video laryngoscopy improves clinical outcomes. It was also revealed, in the largest, prospective randomized controlled trial to date, that there are at least 1% of patients who fail to be intubated even under the video laryngoscope and despite an adequate laryngeal view. In clinical anesthesia, this has become a familiar phenomenon known as “can see [the vocal cords] but can't intubate,” or CSCI.
Confronting such a challenge, some manufacturers are resorting to the assembly of a multitude of devices, with an interchangeable port connected to a common display monitor (e.g., MultiViewScope by MPI Inc, Airway Total Solution by Acutronic AG, C-CAM/C-HUB by Karl Storz AG). All of which enable practitioners to swiftly disassemble a device failed to intubate and mount on another for a renewed attempt.
The algorithm of intubation underlying such an approach follows that an intubationist usually begins with a conventional laryngoscope, then change to VL if that fails, and finally, as shown in the aforementioned clinical trial and elsewhere, switch to the device most often deployed as the last resort, the flexible (fiber optic) bronchoscope (FOB).
Such a sequence, however, under the duress of rapid oxygen desaturation or life threatening emergency, may become suboptimal, if not irrational. Furthermore, the more attempts an intubationist makes, the higher risks for oral pharyngeal injuries would it lead to. Instead of device switching, it seems that an intubation device should strive for successful intubation in the first attempt at any time.
The higher success of the fiber optic bronchoscope in the most difficult intubations is largely owing to the articulable tip that other devices do not possess. FOB is a flexible imager, whose long, thin shaft may be maneuvered to perform snake-like movements passing through between the vocal cords, on which an endotracheal tube (ETT) can be carried over. Coupled with other tools for biopsy or lavage, FOB, originally developed for the tracheal and bronchoalveolar visualization and treatment, is an overly sophisticated instrument, not optimized and priced for tracheal intubation. Its shortfalls as an intubation device are known as the following.
First, due to its flimsy nature, FOB, en route to the vocal cords, may lose its way during lengthy detours inside some treacherous anatomies such as the piriform fossae, instead of passing over them. Consequently, the intubation time under FOB is significantly prolonged, risking the complications of oxygen desaturation. Additionally, the technique of FOB intubation requires a much longer learning curve to master; and, additionally, it can be afforded by few due to its high price tag, currently about $12,000 apiece. An anesthesia service in a typical 300-bed community hospital in the US may even have only one FOB shared with other departments.
This often results in a crisis mode, when the device is demanded by more than one patient with a difficult airway. Nevertheless, in other environments, such as in poorer developing countries, the cost of the device is prohibitive.
Many inventors have since sought simpler alternatives to FOB either on the stylet that assists the entry of endotracheal tube or directly on the tube itself. In 2002, there was a prospective study conducted by the US National Emergency Airway Registry. With 7,712 patients in 30 hospitals of three countries and among six adjunct devices used, the result showed that a tip-articulable ETT named Endotrol (Mallinckrodt) could surprisingly achieve 83% of the success rate of FOB in rescuing the failed intubation. At present day's price, the former is 1/1,000 the cost of the latter, while its associated imaging system is 1/100 the cost.
The Endotrol, also called the “trigger tube”, is the first one-directional, tip-articulable endotracheal tube, proposed almost 40 years ago by Isaac Jackson for nasal intubation (U.S. Pat. No. 4,150,676). It has an index finger pulled nylon control wire threaded through the passageway (a hole) inside the ETT wall. In 1986, Roger Donenfeld conceptually extended it to a four-directional articulable ETT by augmenting the Jackson design to four wires running through four holes (U.S. Pat. No. 4,685,457), though no products have ever been realized. It should be noted, however, that the ETT manufacturing process has since vastly advanced; nowadays as many seven passageways (holes) can be created along the wall of an ET tube.
Recognizing that the poor performance of Endotrol results from its unbendable tip, Toti et al adopted the design element of endoscopes, breaking open a notch on the bending point of ETT, whose product, now marketed as EndoFlex, has significantly enhanced the articulating capability of ETT (U.S. Pat. Nos. 6,321,749; 6,553,993B2; 6,761,171B2).
Despite the above improvements, the Endotrol and EndoFlex remain rarely used products among intubationists, and if FOB as the benchmark, the primary shortfalls of the two special ETTs are two-fold: the first is their incapability of two directional articulations. The only articular direction they can attain is that tip upward from ETT's concave line, which is already achievable by a styletted ETT maneuvered with the right hand—whereas intubation via difficult airways such as the anterior larynx or through the nasal cavity demands such ETTs that can also articulate on the opposite, i.e., the convex direction. It is this very direction, for which intubationists sought FOB help in the first place, that is missing in both EndoFlex and Endotrol. Indeed, realizing FOB can never be afforded ubiquitously handy spawned a body of literature by intubationists to explore such ad hoc techniques as “reverse loading” or 180° rotation of ETT, all for coaxing the tube forward to the other direction.
The second is their incompetence at imaging. The operation of EndoFlex is based on a “puller” and Endotrol on a “trigger” mechanism. Both require the thumb blocking the ETT connector, which practically prevents them from equipping an imager (e.g., inserting a video stylet into the tube). Furthermore, this very style of operation also made EndoFlex and Endotrol as devices un-ergonomic to use—since the most efficient and comfortable way to use an ETT, as favored by the overwhelming majority of intubationists, is the style like holding a pen, which simultaneously enables the tube to be imaging competent.